Fig. 4From: A female patient with retinoblastoma and severe intellectual disability carrying an X;13 balanced translocation without rearrangement in the RB1 gene: a case reportSchematic representation of the XCI pattern and its outcomes with X-A translocation. (a) In a standard X-A translocation, the normal X chromosome is inactivated in 100% of the cells because inactivation of the der(X) often leads to suppression of genes indispensable for cell survival. In this situation, the gene dosage is normal and the carrier has no symptoms. (b) In the present study case, the der(X) was inactivated in a subset of the cells in which 13q genes including RB1 on the der(X) were suppressed. This inactivation does not spread to the 13q terminal because of its long distance from the X-inactivation center, allowing the cells to survive. In der(13), the genes located at Xq28 are active. This results in retinoblastoma, 13q deletion syndrome- and an Xq28 functional disomy-like phenotype in such cellsBack to article page